The present invention is directed to cluster tools for processing wafers and the like, and, more particularly, to a cluster tool architecture to be used, inter alia in sulfur trioxide processing of such wafers.
Cluster tools have been available for many years. Such tools are used for automated processing of semiconductor wafers, for example. FIGS. 1-4 are schematic drawings of prior art cluster tools, and are shown here as an aid to differentiate the present invention from the prior art cluster tools.
FIG. 1 depicts an example of prior art cluster tool architecture, 110, which is similar to a sputtering tool produced by Varian Associates. In this architecture, silicon wafers (not shown) are handled alternately from cassettes 112 and 114. First, the entire cassette assembly is pumped down to vacuum and the substrates are unloaded, one at a time, by means of a vacuum transfer arm 116 to an alignment station 117. The substrates are then loaded with a second arm 118 into one of several process stations 120, 122, 124, or 126, and then out to a de-gas and cool-down station 128 and finally back into the original cassette. This architecture primarily provides a method for integrating several vacuum processes, which can be performed in a random order. The sputtering tool 110 is a vacuum-only processing apparatus.
FIG. 2 depicts a second type of cluster tool architecture 210, similar to the cluster tool manufactured by Applied Materials, which integrates several vacuum processes that must be isolated and performed at different vacuum levels. In this architecture, cassettes 212 and 214 are pumped down from atmosphere, and the wafers are unloaded one at a time, aligned and then reloaded into the process chambers 232, 234, 236, and 238 by means of the vacuum transfer arm 216. In the cluster tool architecture 210, the process chambers are specifically limited to vacuum processes such as chemical vapor deposition (CVD). After CVD, the wafer is loaded into the buffer station 240, where it is purged and further pumped down for lower vacuum processing in sputtering stations 220, 222, 224, and 226, employing vacuum transfer arm 218. After sputtering, the wafer is loaded into a second buffer station 242, where pressure is changed to match the pressure in the area 216 (different vacuum level). The wafer is then cooled down and moved from the buffer station to any of the CVD process chambers 232, 234, 236, or 238 or out of the apparatus into one of the cassettes 213, 214. Cluster tool architecture 210 is a random order processing with two isolated sections. However, it is still a vacuum-processing tool.
FIG. 3 depicts a third architecture 310, which is similar to the tools manufactured by Brooks Automation, PRI, and others. This architecture is based on the concept of staging two or more cassettes 312a, 312b, 314a, and 314b, to unload wafers, one at a time, in atmosphere, using an atmosphere transfer arm 316. The wafers are aligned, if required, at flat-finding station 317 before being loaded into the buffer station 340, which is then pumped down to vacuum. Once the buffer station 340 is at vacuum, a second vacuum robot 318 unloads the buffer station and loads the wafer, in random order, to the first available vacuum process chamber 320, 322, 324, or 326. After processing, the wafers are removed and loaded into the second buffer station 342 to be vented back to atmosphere and loaded to its original cassette or any available cassette 312a, 312b, 314a, or 314b. 
FIG. 4 depicts an example of a forth prior art architecture 410 which combines vacuum and atmospheric processing in a linear architecture, similar to the architecture employed in the Lam Research metal-etch tool. Here, the wafer is unloaded from the cassette 412, aligned at an aligner 417, and loaded into a buffer station 440, which is pumped down to vacuum. Subsequently, the wafer is loaded into a plasma etch chamber 420 (in vacuum) for processing, and is moved into a separate buffer station 442 for venting to atmosphere. After venting, the wafer is loaded to a clean station 444 where the wafer is rinsed or scrubbed with water, at atmosphere, and then dried and loaded into an exit cassette 446. The prior art architecture 410 provides a linear processing sequence that is inflexible to accommodate variations in the processing steps.
The disadvantages of prior art approaches are:
1. cluster tool processing is done only in a vacuum environment;
2. the atmospheric section of the cluster tool does not integrate atmospheric processing in a cluster format; and
3. tool architectures that have integrated vacuum and atmospheric processing have done so in a linear work flow format. This linear architecture does not allow wafers to return to an original slot in the cassette. Neither does it allow a plurality of processing chambers for parallel processing, in order to achieve a higher throughput.
Processing of wafers using sulfur trioxide is the subject of U.S. Pat. No. 5,037,506, issued Aug. 6, 1991, and U.S. Pat. No. 5,763,016, issued Jun. 9, 1998. Automated processing of wafers with sulfur trioxide requires controlled atmospheres prior to, during, and subsequent to the exposure to sulfur trioxide, due to the various processing steps involved.
However, the prior art architectures are unable to perform sulfur trioxide processing. All known prior art tools, with the exception of Brooks/PRI tool (FIG. 3), transfer wafers under pumped down conditions and all of the processing takes place in vacuum or a reduced atmosphere environment. In the Brooks/PRI tools, while wafer cassettes are unloaded in atmosphere, no atmospheric processing is performed. The Brooks/PRI architecture""s intent is to load substrates to a vacuum processing cluster tool from a number a multiple of wafer cassettes staged in atmosphere.
Thus, there is a need for a cluster tool architecture to process wafers in the presence of sulfur trioxide, or other reactive gases such that it permits: (1) loading the wafers in an atmospheric-cluster environment, (2) performing one or more atmospheric processes, (3) exchanging wafers between atmospheric and vacuum environments, (4) random order processing using a multiple of vacuum-compatible processing stages, (5) returning the waters to the atmospheric-cluster environment for additional atmospheric processing, and (6) finally returning the wafers to an exit cassette or the original cassette slot.
In accordance with the present invention, a cluster tool architecture and method are provided for processing substrates by exposure to sulfur trioxide and other process environments, as well as prior and subsequent treatments thereto. The cluster tool architecture comprises:
(a) an atmospheric processing area, maintained at atmospheric pressure;
(b) cassette means for introducing a plurality of the substrates into the atmospheric processing area;
(c) at least one process station in the atmospheric processing area for exposing the substrates to a first process environment;
(d) an enclosed vacuum processing area, maintained at a vacuum pressure;
(e) a first buffer station between the atmospheric processing area and the enclosed vacuum processing area to pump and vent from atmospheric to vacuum pressures and transition the substrates from the atmospheric processing area to the enclosed vacuum processing area;
(f) at least one process station in the enclosed vacuum processing area for exposing the substrates to a second process environment;
(g) a second buffer station between the enclosed processing area and the atmospheric processing area to re-pressurize from vacuum to atmospheric pressures and transition the substrates from the enclosed vacuum processing area to the atmospheric processing area;
(h) an atmospheric transfer arm in the atmospheric processing area for transferring the substrates from the cassette means between one of the buffer stations and at least one process station in the atmospheric processing area and then to the cassette means; and
(i) a vacuum transfer arm in the enclosed vacuum processing area for transferring the substrates from the one of the buffer stations to one of the process stations in the enclosed vacuum processing area and from that process station in the enclosed vacuum processing area to the one of the buffer stations, wherein both buffer stations are equally accessible to both the atmospheric transfer arm and the vacuum transfer arm.
The first process environment can comprise a pre-processing step, such as cleaning and rinsing the substrate, or it can comprise atmospheric-compatible physical or chemical process steps prior to entry into the enclosed vacuum processing area and/or it can comprise a post-processing step subsequent to processing of the substrate in the enclosed vacuum processing area.
The second process environment can comprise sulfur trioxide, a CO2 blast, plasma, or other chemically or physically reactive environments.
The invention disclosed and claimed herein is an improvement over previous art in that it:
1. integrates atmospheric or high pressure processing with vacuum processing;
2. allows random access through integration, so there is a freedom of programming process flow;
3. allows re-entry of substrates, in that process steps can be repeated at any time; and
4. allows substrates to be replaced back into the cassette of origination or predetermined exit cassette after the process is complete.
The cluster tools of the prior art achieve some of these features, but none can achieve all of the features. While some prior art cluster tools appear to be similar to the cluster tool disclosed and claimed herein, such cluster tools integrate atmospheric handling, a large number of cassettes in atmosphere, and vacuum automation, and do not deal with atmospheric processing in conjunction with vacuum processing. Specifically, the main feature of the cluster tool of the present invention is that processing for any known semiconductor process can be integrated in a single substrate at a time, in a cluster format. This feature is not believed to have been done before, to the knowledge of the inventor.
Indeed, the processing cluster tool of the present invention may appear to be similar to the linear Lam tool (FIG. 4), in that the substrates are loaded from atmosphere to buffer, which brings the substrates into the vacuum environment for processing, then vented back to atmosphere for subsequent atmospheric processing. However, the difference between the tool of the present invention and the Lam tool is that in the tool of the present invention, the substrates are loaded and unloaded in a random access architecture of a cluster tool. By xe2x80x9crandom access architecturexe2x80x9d is meant that the substrate flow goes to the first available station, and does not follow a pre-defined, fixed route. The Lam tool is a linear format in which substrates go from an input cassette to an exit cassette. The tool of the present invention is a random access tool in which substrates go from an input cassette back to the original slot in that cassette on output.
Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings, in which like reference designations represent like features throughout the FIGURES.